













THE BRITISH FERNS. 
Genus IX: CETERACH, Willdenow. 
GEN. CHar.—Sori linear oblong, obsoletely indusiate; the recep- 
tacles lateral, occupying the anterior (i. e. anterior as regards the 
segments) side of the veins, or posterior in the basal sori of each 
segment, at first hidden amongst densely imbricated chaffy scales. 
Indusium obsolete: * linear narrow plane sometimes obsolete" 
(Hook.). Veins forked, from a central costa; venules sub-parallel, 
soriferous below, anastomosing irregularly near the margin, the basal 
anterior ones (i. e. anterior as regards the frond) soriferous on the 
side next the rachis or primary costa; marginal veinlets mostly free. 
Fronds pinnatifid, coriaceous, densely clothed beneath with 
imbricated chaffy scales. 
Caudex short, erect, tufted. 
This genus is one of anomalous character, having peculiarities in 
its fructification which seem to unite it both with the Aspleniee and 
the Gymnogramme. Thus, it agrees with the latter group in having 
the sori destitute of an evident indusium, this organ being repre- 
sented, according to the observations of some botanists, by a slightly 
elevated membranous ridge behind the sorus. Mr. W. Wilson 
finds evident traces of an involucre on the lower side of the sorus, 
namely, a “narrow membrane fringed with the same chaffy scales 
which cover the back of the frond.”* Dr. Deakin, who states + that 
he has examined with great care many specimens at different periods 
of development, finds only a slightly elevated or narrow projecting 
line, which ean at most be called an obsolete indusium ; and this 
disappears at a later stage. Even this, however, is not always 
to be seen, or at least cannot always be satisfactorily made out. 
The cover to the sorus, which is one of the marks of the Asplenieœ, 
may therefore be said to be constantly in an abortive state, if not 
absent, and hence it is described as being obsolete. 
* Hooker, British Flora, 5 ed. 436. 
+ Deakin, Florigraphia Britannica, iv. 83. 

